The present invention relates to a semiconductor light emitting device.
Semiconductor light emitting devices such as laser diodes, surface-emitting LEDs and edge-emitting LEDs are capable of efficient high-power operation and high-speed modulation and these advantageous features are utilized for optical fiber communications. Since the efficient utilization of input current for the generation of optical output depends largely on the structure by which the input current is concentrated for injection to an active layer, many proposals have hitherto been made for the current concentration structure.
Although light emitting devices at present operate satisfactorily at low frequencies, high frequency operation is not satisfactory in terms of response characteristics and thus the modulation characteristic of the device is severely limited. In laser diodes having a current blocking layer in proximity to an active layer, current at high frequencies would leak to the uppermost semiconductor layer due to its low spreading resistance, resulting in an increase in the parasitic capacitance associated with the p-n junction of the current blocking layer and hence in a poor high-frequency modulation characteristic. Likewise, the surface-emitting LEDs suffer from the same problem.
It has been proposed to construct light emitting devices with an insulating layer deposited on the uppermost semiconductor layer outside the current injection region to reduce the parasitic capacitance (see Manuscript 25a-P-8, The 44th Symposium of the Institute of Applied Physics of Japan). However, the partial deposition of an insulating layer causes a mechanical stress at the inner circumference thereof and accelerates the deterioration of the active layer. Similar efforts involve the bombardment of protons instead of the deposition of insulating layer as described in Electronics Letters, 25th October 1979, Vol. 15 No. 22. This method also proves unsatisfactory in that the proton bombardment destroys the crystal structure of the semiconductor layers.